Air-cooled blade



July 28, 1959 J. c. FRECHE AIR-COOLEDM BLADE Filed Sept. 28. 1955 x. I IP7117515 FIG. 3

I INV ENT OR JOHN a. FREGHE ATTORNEYS United States Patent UnitedStates;of America-as represented by the Secretary of the Navy ApplicationSeptember 28, 1955, Serial No. 537,313

1 Claim. (Cl. 25339.1'5)

(Granted under Title 35, US. Code (1952), sec. 266) The inventiondescribed herein may be manufactured and used byor for the Government ofthe United: States of America for governmental purposes without thepayment of any royalties thereon or therefor.

This invention relates to air-cooled blades for turbines, compressors,blowers and the like where light Weight is an important consideration.

Turbine blades are commonly made of an impermeable metal shell attachedto a heavy metal base as by welding or brazing. This shell must besufiicient-ly strong not only to support its own mass at the highturbine rotor speeds but also, in many cases, to support internal finsor tubes inserted to facilitate heat transfer. Alternately, a lightblade shell may be used by inside the shell is inserted a massivesupporting strut which is integral With blade base. The strut and base,thus, form a solid block of metal having approximately the same mass asa standard uncooled turbine blade. In either type of blade, as abovedescribed, the manufacturing processes are complex and the relativelyhigh weight of the blade results in large wheel rim loading and heavyrotors.

A primary object of this invention is to provide a blade for turbinesand the like which is light in weight permitting important reductions inrim loading and overall rotor weight.

Another object is to provide a turbine blade which may be entirelyfabricated by simple techniques from stampings, castings or formedparts.

An additional object is to provide a light-Weight blade which lendsitself readily to efficient air cooling.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes betterunderstood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

Fig. 1 is a perspective view of a turbine blade with the outer shellpartly broken away to show the rib construction;

Fig. 2 is a detail view showing the blades attached to the turbinerotor;

Fig. 3 is a detail view of a blade rib and also showing the ribrelationship to the blade shell, base shell and spacer plate; and

Fig. 4 is a side elevation of the blade with the airfoil shell brokenaway taken along lines 4-4 of Fig. 1.

For ease of description, the blade has been illustrated and will bedescribed as applied to a turbine. In Fig. 2, the rotor of the turbineis indicated, with blade units 11 attached thereto. The rotor is formedwith a series of radial air ducts 12 which communicate with thepressurized air supply system (not shown). Each of these ductsterminates at the rotor periphery in a transverse blade attachmentgroove 13 having sigmoid walls, thus providing the groove cavity with alateral constriction 14 placed at about one-half the groove depth whichc0- operates with the lib plates 30 to secure the blades in the grooves.

The blade unit 11 is formed of four elements, the shell ice 20, the-ribs21- for-supporting the shell, the spacerplates 22 for spacingthe-ribs,--and the base plate 23'; The air foil shell 20'is shaped' 'tom'eettheaero'dynamic requirementsfor' eflective' turbine use witharounded'leading edge 24 and'a th'inner tr'ailin'gedgathe edges beingjoined by con'cavo-convex side plates 26 and 27, giving the requiredcamber.

Supporting the shell- 20 are a plurality of flat strips forming parallelribs 21-. The'faces 19 of ribs-21 extend across theblade-depth andarespaced-fro'm'eachother to'form' coolant'ducts, the depth of the facesof each rib being-equal to'the blade depth atthepoint of rib locationand consequently differing-in depthfrom each other. The base of each n'bterminates -in -arib' plate 30, which'con form's in'= edge outline to*'that ofjthe rotor groove 1 3; so' that 'each' plate 30 and rib 2 1 maybe moved into mat ing engagement with groove 13. These rib plates 30 areseparated from each other by suitable rectangular spacer plates 22,preferably placed at the inner ends of the rib plates 30, as shown inFigs. 1 and 4 and uniformly apertured, as at 40, to permit air flow fromrotor ducts 12. To bind the shell and ribs together and to preventcoolant leakage, the base plate 23 is applied to the base of the airfoilshell 20. This base plate is shaped to overlie closely the upper edges18 of the rib attachment plates 30 and has an aperture 16 conforming incontour to the external surface of the airfoil shell 20. The base plate23 is provided with an upstanding flange 17 around the aperture 16 whichengages the lower external surface of the airfoil shell to prevent thecoolant from escaping from the blade interior. The leading and trailingedges of the base plate are down-turned at 41 to engage a portion of thecorresponding edges 18 of the rib plates 30 as shown in Figs. 2 and 3.As shown in Fig. 2, the edges 18 project beyond the outer periphery ofthe rotor when the plates 30 are engaged in the grooves 13 with theedges 41 of the base plates engaging the peripheral surface of the rotorthereby preventing coolant leakage between the plates 30 and the rotor.

In the final assembled form of the blade, the various component partsare permanently fixed together, as by welding or brazing, to form arigid blade unit entirely free of weight concentration in the base andyet possessing ample strength for high speed use. The rib spacing, also,permits free access of cooling air from rotor ducts 12 to all parts ofthe blade interior, insuring adequate shell cooling. Particularattention is directed to the fact that apertures 40 are of equaldimensions and hence, the amount of coolant entering each rib duct isthe same. However since the depth of ribs 21 varies with the contour ofairfoil shell 20, being lesser at the leading and trailing edges of theblade where the heat effects are greatest, the rib ducts at these edgesare of reduced crosssection. As a result, the velocity of coolant isgreatest at the leading and trailing edges of the blade and, hence, thecooling action is most eflicient at these points of the blade structure.In addition, the elements of the blade are such as to lend themselvesreadily to stamping, casting or forming procedures permitting rapidassembly-line production of the blades.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claim the invention maybe practiced otherwise than as specifically described.

What is claimed is:

A rotor for turbines and the like comprising a rotor having a rim withcircumferentially spaced grooves ex tending across the periphery of saidrim, said grooves having side walls curved reversely inward and radiallyextending air ducts formed in the rotor and connected with the groovesto supply coolant thereto, and a lightweight blade mounted radially onthe rdmifim, said blade comprising a plurality of flat strips formingribs, said ribs being positioned in parallel face-to-face relationshipand spaced apart substantially along the chord of the blade, the depthof the faces of said ribs-progressively increas: ing from the end ribsto the intermediate ribs, a thin, concave-convex, impermeable aircraftfoil shell enclosing and attached to the side edges of said ribs, theshell and rib faces cooperating to form coolant channels, the channelsat the leading and trailing edges of said blade having transverse areasreduced over those of intermediate chan; nels whereby the velocity ofcoolant in said channels will be a maximum at the leading and trailingedges, the bottom of each rib terminating in a rib plate, the rib plateshaving a shape complementary to the curved walls of said spaced groovesand cooperating with said grooves to secure the blade to the rotor rim,the upper edges of said rib plates projecting beyond the surface of therotor rim when the blade is secured thereto, thin, flat spacer platespositioned between said rib plates whereby said ribs are inequally-spaced relationship, said spacer plates being uniformlyapertured to permit equal coolant flow in each channel, and a base plateoverlying the upper edges of said rib plates, said base plate having anaperture with a narrow, upstanding flange conforming in contour to theexternal surface of said shell, saidbase plate being permanently securedto said upper edges of said rib plates and said flange being permanentlysecured to the base of said shell, said base plate further havingturn-down edges which engage the surface of the rotor rim whereby, thecoolant is prevented from escaping from said ducts and from saidchannels.

References Cited in the file of this patent UNITED STATES PATENTS2,656,146 Sollinger Oct. 20, 1953 FOREIGN PATENTS 860,438 Germany Dec.22, 1952

